Diabetes is a term that refers to a collection of diseases resulting in disordered energy metabolism and varying degrees of blood glucose elevations or hyperglycemia. One of the best characterized forms of the disease is that resulting in immunologically mediated destruction of the insulin secreting pancreatic beta cells. This severe form of the disease is termed Insulin Dependent Diabetes (IDD) since it is associated with progressive insulin deficiency and coincident symptoms such as weight loss, glycosuria and polyuria, and increased thirst or polydipsia. Other terms for this form of diabetes are Type 1 Diabetes (cf. Type 2 Diabetes which results from an inherent resistance to insulin action); Ketosis Prone Diabetes because there is abnormal generation of ketone bodies as a result of excessive breakdown of body fats due to the severe insulin deficiency, or Juvenile Diabetes, since virtually all diabetes that appears in childhood and adolescence is of this type (see Atkinson and Maclaren, N Engl J Med 1994:331:1428-1436).
Diabetes is a major public health problem, especially in Western countries. The incidence rates vary greatly worldwide, from as high as 40 per 100,000 persons in Finland to as low as 1-2 per 100,000 among Japanese, with the US in between. The peak incidence is during the pubertal years associated with increasing bodily demands for insulin associated with muscle growth. The prevalence rates in the US population under age 20 years is 0.25% and it approaches 0.4% over a lifetime, albeit an estimated 10-20% of patients with Non Insulin Dependent Diabetes (NIDD) or Type 2 or Maturity Onset Diabetes also have, in reality, slowly progressive IDD. Thus, it is estimated that there should be at least 1 million Americans affected by IDD.
Diabetes results in progressive damage to the blood vessels of the body, to a degree that depends upon the severity of hyperglycemia and its duration. The incident mortality rate for IDD has been calculated to be 7 fold higher than for age matched non diabetic controls. Whereas the decade long Diabetes Control and Complications Trial (DCCI) concluded in 1994 by the National Institutes of Health in the US showed that meticulous insulin replacement therapy would slow the appearance of damaged arteries, it was not able to prevent this since blood glucose levels were never kept within normal limits. Ocular complications of diabetes are the leading cause of new blindness in persons of 20-74 years of age. The risk of lower extremity amputation is 15 fold higher in those with diabetes, while more than half of the approximately 125,000 persons undergoing lower limb amputation do so as a direct consequence of diabetes. Approximately 40% of persons undergoing renal transplantations have kidney failure because of their diabetes, and the proportion due to diabetes continues to rise each year. Women with diabetes produce newborn infants with a 7% newborn mortality rate, albeit this outcome can be greatly improved with tight glycemic control during the gestation period. Other complications of diabetes include increased heart disease and stroke, loss of nerve cells or neurones innervating the limbs and intestine, impotence and infertility, cataract formation in the lens of the eyes, increased periodontal disease, and predisposition to infectious diseases especially from bacteria and yeast. Of all patients with diabetes, those with IDD have a disproportionate share of these complications because of its severity and usual early age of onset In the US, the direct health care costs attributable to diabetes in 1994 have been estimated to exceed $120 billion. Thus it is important that the pathogenesis of IDD be understood and strategies be developed to prevent it as a fully expressed clinical disease.
Patients with IDD are unusually prone to other diseases that have become recognized to have autoimmune origins. These diseases include thyroiditis or Hashimoto disease, Graves disease, Addison disease, atrophic gastritis and pernicious anemia, celiac disease and vitiligo (Maclaren, Diabetes Care 1985:8 suppl:3438). Evidence that IDD itself has an autoimmune nature began with histological studies of patients that succumbed at diagnosis which indicated that the islets were infiltrated with a chronic inflammatory (lymphocytic) infiltrate termed insulitis. This was supported in the early 1970""s by reports of islet cell autoantibodies reactive to antigens within the cytoplasm (ICA) (Lendrum et al. Lancet 1975:1:880-882) or confined to the islet cell surfaces (ICSA) (Maclaren et al. Lancet 1975:1:977-1000) as detectable by indirect immunofluorescence. Later it was recognized that many patients also develop autoantibes to insulin (IAA) before their diagnosis (Pahner et al., Science 1983:222:1337-1339) as well as to insulin receptors (Maron et al., Nature 1983:303:817-818). Autoantibodies were also reported to an islet cell protein composition of 64,000 M.Wt. in man (Baekkeskov et al., Nature 1982:298:167-169), in the Biobreeding (BB) rat model (Baekkeskov et al., Science 1984:224:1348-1350) and in the Non Obese Diabetic (NOD) mouse model (Atkinson and Maclaren, Diabetes 1988:37:1587-1590). This 64 KDa antigen has subsequently been reported to be the lower molecular weight isoform of glutamic acid decarboxylase (GAD65) (Baekkeskov et al., Nature 1990:347:151-156) (Kauffman et al., J Clin Invest 1992: 283-292). GAD is an enzyme that converts glutamate into the membrane stabilizing neurotransiitter called gamma amino butyric acid or GABA. In addition to autoantibodies to GAD, peripheral blood mononuclear cells were shown to be autoreactive in patients developing IDD (Atkinson and Maclaren et al., Lancet 1992:339: 458-459, and Harrison et al. Lancet 1993:341: 1365-1369). Indeed a leading possible cause for IDD is that immunity to enteroviral proteins (developed through infection by Coxsackie or closely related viruses) that have structural homologies to GAD, may in the genetically predisposed individual, trigger an autoimmune response to islet cells because of this molecular mimicry (Atkinson and Maclaren, Scientific American 1990:262:61-71; Kauffman et al. J Clin Invest 1992:89: 283-292; Atkinson, Maclaren et al., J Clin Invest 1994:94: 2125-2129).
Since the above immunological markers predate the clinical onset of IDD often by many years, their possible value in disease prediction became increasingly realized (Maclaren, Diabetes 1988:37:1591-1594), permitting in turn options for therapeutically induced delays in diabetes onset to be considered (Muir and Maclaren, J Autoimmunity 1993:16:301-310). Indeed by 1994, multicenter trials attempting to prevent IDD through prophylactic parenteral insulin or oral insulin therapies had been initiated in the US (the DPT-1 trial), as well as in Europe using prophylactic nicotinamide (the ENDIT trial). Among relatives, the appearance of LAA was shown to predate onset of IDD (Atkinson and Maclaren, Diabetes 1985:35: 894-898) while ICA proved to be valuable to the prediction of IDD in relatives (Riley, Maclaren et al., N Engl J Med 1990:323: 1167-1172) as well as in the general population (Schatz, Maclaren et al., J Clin Invest 1994:93: 2403-2407), as modifiable on the basis of coincident IAA (Krischer, Maclaren et al., J Clin Endo Metab 1993:77: 743-749). While not ideal the predictability of IDD based upon the ICA test provided the basis for the DPT-1 and ENDIT trials mentioned above. Furthermore, autoantibodies to the 64KDa islet cell protein also proved to have utility in IDD prediction (Atkinson, Maclaren et al., Lancet 1990:335: 1357-1360), as eventually realized by the chemical assay for autoantibodies to GAD65. (Schott, Maclaren et al., J Autoimmunity 1994:7:865-872). These studies made it important to resolve the nature of all of the islet cell autoantigens involved in the pathogenesis of IDD (Atkinson and Maclaren, J Clin Invest 1993;92:1608-1616). Whereas ICA, as determined by indirect immunofluorescence of human cryocut pancreatic sections, was likely to represent multiple autoantigens (Genovese et al., Diabetologia 1992:35:385-388), GAD soon proved to be one of these (Atkinson, Maclaren et al. J Clin Invest 1993:91:350-356). Insulin, however, was not a component of ICA unless the pancreatic sections were first chemically xe2x80x9cfixedxe2x80x9d before being used as tissue substrate.
Recently, a 3.6-kb cDNA with a 2,937-bp open reading frame was isolated from a human insulinoma subtraction library (ISL-153) as described by Lan et al. (1994, DNA and Cell Biology, 13:505-514, herein incorporated by reference). The predicted amino acid sequence and in-vitro-translated product of IA-2 cDNA revealed a 979-amino acid protein with a PI value of 7.09 and a molecular mass of 105,847 daltons. The protein sequence is consistent with a signal peptide, an extracellular domain, a transmembrane domain and an intracellular domain. The extracellular domain contains an unusual cysteine-rich region following the signal peptide. The intracellular cytoplasmic domain of IA-2 possesses highly conserved regions similar to the catalytic domains in members of the protein tyrosine phosphatase (PIP) family. Northern blot analyses showed that IA-2 MRNA was expressed in five of five freshly isolated human insulinomas, rat and mouse insulinoma cell lines, and in enriched normal mouse islets. It was also found in normal human brain, pituitary, pancreas, and brain tumor cell lines, but not in a variety of other normal or tumor tissues. Based on the sequence and expression data, it appears that IA-2 is a new member of the receptor-type PTP family that is expressed in islet and brain tissues. The involvement of the molecule in beta cell autoimmunity or IDD was queried but was not disclosed or suggested in that work.
The invention described herein concerns a novel means of accurately detecting the early stages of IDD, such that risk for the disease can be assessed. Also described are means of treating IDD and thereby preventing the occurrence of its clinical manifestations.
It has been found that autoantibodies to islet cells (ICA) can be used as important predictors of IDD. However, their predictive value in individuals found to have them is quite variable. When found in the absence of IAA, they give an overall predictability for IDD of about 1 in 4 over 5 years, but the rate of progression to IDD rises up to 2 in 3 when found together with IAA, at least in non-diabetic relatives of patients with IDD (Krischer, Maclaren et al 1994: J CGn Endo Metab 1993: 77:743-749). Among non diabetic relatives of families affected by IDD who are under the age of 10 years when ICA are discovered, ICA strongly predict IDD (Riley, Maclaren et al. N Engl J Med 1990:323:1167-1172). The instant invention is based on the component autoantibodies and autoantigens that comprise the ICA reaction, which provide differential information as to the degree of predictive power of ICA, Appearance of these component autoantbodies aids in the identification of the stage of the disease and thus in the time to clinical diagnosis. The indirect immunofluorence based ICA test is cumbersome to perform, and does not replicate as well as chemically based assays. One component of the ICA reaction is that explained by autoantibodies to GAD65, and this latter determination has become available through immunoassays.
The instant invention identifies a second autoantibody component of the ICA reaction, which is directed to a an islet cell member of the receptor type of the tyrosine phosphatase family, termed IA-2. We identify the human IA-2 gene product as a major autoantigen of importance to IDD. We sequenced and cloned the IA2 gene, and expressed the gene product in rabbit reticulocytes, to detect the corresponding autoantibody. Detection of autoantbodies to the GAD65 and to IA-2 antigens effectively substitutes for the cumbersome and less than completely reliable ICA assay with a reliable, chemically based assay. Further, the availability of recombinant IA-2 permits the antigen to be used alone or in combination with other antigens in a therapeutic regimen to delay the onset or progression of clinical IDD.
A further embodiment of the subject invention concerns the use of fragments of the full-length IA-2 molecule to detect antibodies to IA-2. Such fragments would, preferably, be larger than the fragment known as ICA 512 as described by Rabin et al. (Rabin et al., Journal of Immunology 1994:152:3183-3188).
Accordingly, it is an object of this invention to provide methods and compositions for the immune detection of insulin dependent diabetes and susceptibility to IDD.
Another object of the invention is to provide methods and compositions for the immunoprophylaxis and treatment of IDD. Other objects of the invention will become clear from the complete disclosure.
The invention described here relates to the detection of antibodies to insulin antigen-2 (IA-2), alone or in combination with other antigens, as an accurate and specific early indicator of the onset of Insulin Dependent Diabetes (IDD).
IA-2 has been recently identified as a member of the transmembrane protein tyrosine phosphatase family. The complete amino acid sequence of IA-2 has been determined and the protein can be expressed as described herein in bacteria or eukaryotic cells.
Of sera from 55 diabetic patients, 45.4% reacted by ELISA with IA-2 expressed as intracellular and extracellular components in E. coli as compared to only 7.5% of normal controls. Analysis of newly-diagnosed (less than one year) IDD patients revealed that 50% reacted with IA-2 as did 38% of patients with longer term diabetes. Reactivity of IDD sera with glutamic acid decarboxylase (GAD65) as compared to reactivity with IA-2 showed that 60% of GAD65-negative IDD sera were positive for IA-2. Further experiments revealed that both rabbit antibody raised to IA-2, and human IDD sera positive for IA-2 antibody and affinity purified by passage through an IA-2 column, specifically stained cells in the pancreatic islets of Langerhans, but not surrounding acinar tissue.
One aspect of the subject invention is the discovery that IA-2 is an autoantigen in IDD and is responsible for some of the staining of islets by islet-cell autoantibody positive sera, especially those negative for reactivity to the GAD65 antigen. These findings suggest that testing for autoantibodies to both GAD65 and IA-2 can be used to provide a reliable method for identifying IDDM patients using chemical assays which are more reproducible than possible using the indirect immunofluorescence for ICA.
IA-2 is a 105,847 kDa transmembrane protein that belongs to the protein tyrosine phosphatase family. Immunoperoyidase staining with antibody raised against IA-2 confirms that this protein is expressed in human pancreatic islet cells. In one embodiment of the subject invention, the full-length cDNA clone of IA-2 can be expressed in a rabbit reticulocyte transcription/translation system and the recombinant radiolabelled IA-2 used as an antigen to detect autoantibodies by immunoprecipitation.
IA-2 can be expressed and isolated and used as an antigen to produce immune tolerance and immunosuppression to ameliorate or prevent IDD. The IA-2 may also be introduced into a patient with an adjuvant, such as alum or any other adjuvant accepted for introduction into people. Furthermore, the antigen can be expressed in a recombinant viral vaccine or the DNA coding for IA-2 could be introduced into an individual for expression in muscle or other cells to achieve immune tolerance and thus prevent or ameliorate IDD.
One hundred coded sera were tested by this method, 50 from patients with newly diagnosed IDD and 50 from age-matched normal controls. Sixty-six percent of the sera from patients, but none of the sera from controls, reacted with IA-2. The same diabetic sera tested for autoantibodies to glutamic acid decarboxylase (GAD65Ab) by depletion-ELISA and to islet cells by indirect immunofluorescence showed 52% and 68% positivity, respectively. Up to 86% of the IDD patients had autoantibodies to IA-2 and/or GAD65. Patients diagnosed with IDD before age 20 were more likely to have autoantibodies to IA-2 than patients diagnosed after age 20. Over 90% (14 of 15) of sera that were ICA-positive, but GAD65 Ab-negative, had autoantibodies to IA-2. Absorption experiments showed that the immunofluorescence reactivity of sera containing ICA was greatly reduced by prior incubation with recombinant IA-2 or GAD65 when the respective antibody was present. It is concluded that IA-2 is a major islet cell autoantigen in IDD pathogenesis, and is responsible, in part, for the reactivity of ICA with pancreatic islets. Tests for the detection of autoantibodies to recombinant IA-2 and GAD65 have advantages over ICA as a predictor and identifier of patients with IDD.
Full-length IA-2 cDNA expressed in a eukaryotic expression system, can be used to create a radioimmunoassay for detecting autoantibodies to IA-2. Two thirds of our IDD patients had autoantibodies to IA-2, as compared to none of the controls. The radioimmunoassay is considerably more sensitive and specific than an ELISA test which employs the full-length of the intracellular domain of IA-2. Moreover, the radioimmunoassay used here is a liquid-phase assay and is therefore more likely to detect conformational epitopes than solid-phase ELISA. Fragments of the full-length protein can also be used.
Following are examples which illustrate procedures, for practicing the invention. These examples should not be construed as limiting. All percentages are by weight and all solvent mixture proportions are by volume unless otherwise noted.